AI slop
Why does AI use so many em dashes?
Why ChatGPT and other AI models filled their writing with em dashes, what the numbers show, why the newest models stopped, and what to write instead.
Short answer: No AI company has published a reason. The likeliest ones: chatbots learned to write from edited books and journalism, where the em dash is common, and they were tuned toward a punchy style that people rated well. By summer 2025, more than half of ChatGPT’s replies had an em dash, up from fewer than 1 in 10 a year earlier. The newest models of 2026 have nearly stopped, but readers still take an em dash as a sign of AI, so in a short reply it costs you trust.
Hyphen, en dash and em dash
They look alike, and each has its own job.
- The hyphen - joins words: well-known, follow-up. It’s the key next to zero.
- The en dash – marks a range, so 9 to 5 becomes 9–5.
- The em dash —, the widest, breaks a sentence: an aside, a sudden turn, or a pause before the point.
An em dash is most often used to indicate a pause in a sentence.
Style guides argue about the spaces around it, never about the mark itself. Plenty of good writers have always loved it.
How often AI uses em dashes
In 2025, The Washington Post looked at 328,744 ChatGPT messages that people had shared publicly.
A year ago, fewer than 1 in 10 ChatGPT responses used an em dash. [...] by summer, more than half of its responses included an em dash.
That jump made the em dash one of the best known signs of AI writing. Online, people started calling it the “ChatGPT hyphen”.
Why AI uses so many em dashes
The companies haven’t said, so everything below is an explanation from the outside. Three come up most.
It learned from edited writing
A language model writes by predicting the next word from what it has read, and the writing it learns most from is edited: books, newspapers, essays. Those use the em dash a lot.
Many of the highest-quality tokens from this training data contain the em dash.
The engineer Sean Goedecke goes further. His best guess is that newer models learned from scanned print books from the late 1800s and early 1900s, which use about 30% more em dashes than English prose today. He says himself that it is “still largely based on speculation”. His post walks through the theories he ruled out.
It was tuned toward a style people liked
After a chatbot learns to write, it is tuned on answers that people rate. An em dash makes a line sound sure of itself, the way an ad does, and answers that sound sure of themselves tend to get good ratings. Wikipedia’s guide to spotting AI writing describes chatbots putting em dashes where a person would use a comma, a colon or parentheses, to give the line a sales pitch feel.
Formatting leaking into sentences
A 2026 paper by E. M. Freeburg argues that the em dash is what’s left of the bullet points and headings chatbots use, squeezed into a sentence. The paper is a preprint, and its author says the link to tuning wasn’t tested on its own.
Then the em dashes went away
On November 14, 2025, OpenAI’s chief executive posted a fix for people who wanted ChatGPT to stop:
If you tell ChatGPT not to use em-dashes in your custom instructions, it finally does what it’s supposed to do!
That still needed an instruction. The models released in 2026 changed by default. A study published on October 1, 2026 compared ten models with human articles on the same topics:
Opus 5.5 uses 0.015 em dashes per 1,000 words, compared with 2.92 for Opus 5, a decrease of 99%.
The same study found OpenAI’s newest model using them 95% less often than GPT-5. Wikipedia’s editors now file the overuse of em dashes under historical signs of AI writing, for 2022 to September 2026.
Why an em dash still reads as AI
Readers spent three years learning that an em dash means a chatbot, and that doesn’t fade in a month. Not every app runs the newest model, either.
In a long article, one em dash is easy to forgive. In a two line reply under a busy post, it’s often the first thing a reader notices, and some of them stop reading there. Writers who used em dashes for decades now get told they sound like ChatGPT.
On its own, an em dash proves nothing. Wikipedia’s guide says a mark like this counts only next to other signs of AI writing. For what those signs are, see what AI slop looks like in writing.
What to write instead of an em dash
| What the em dash does | What AI writes | Write this instead |
|---|---|---|
| Sets off an aside | The launch — three weeks late — went fine. | The launch went fine, three weeks late. |
| Adds a pause before the point | We shipped it — and nobody noticed. | We shipped it. Nobody noticed. |
| Introduces an explanation | One thing changed — the price. | One thing changed: the price. |
| Joins two thoughts | It’s slow — but it works. | It’s slow, but it works. |
A comma, a period, a colon or a plain “and” covers almost every em dash. Two short sentences often read better than one long one.
Should you stop using em dashes?
That’s up to you. In essays and fiction, the em dash has been around for centuries, and careful writers will keep using it.
In replies on social media, we leave them out. Twick’s drafts never contain an em dash or an en dash, because a reply that reads as AI loses the reader before the second line. If you’d like to see the rest of what Twick keeps out of a reply, here’s the Twitter reply generator.
Questions
Does an em dash mean AI wrote it?
No. People used em dashes for centuries before chatbots. It only adds weight to other signs.
How do I stop ChatGPT from using em dashes?
Add it to your custom instructions, for example “Don’t use em dashes.” Since November 2025, ChatGPT follows that instruction, according to Sam Altman.
Do newer AI models still use em dashes?
Far fewer. The study from October 2026 found the newest models from Anthropic and OpenAI using them a small fraction as often as the models before them.
How do you type an em dash?
On a Mac, press Option, Shift and the hyphen key together. On Windows, hold Alt and type 0151 on the number pad. Many apps also turn two hyphens in a row into one.
What’s the difference between an em dash and an en dash?
Length and job. The en dash is the width of a letter n and marks ranges. The em dash is the width of an m and breaks a sentence.